Method for controlling with adaptivity a wastegate in a turbocharged internal combustion engine

ABSTRACT

A method for controlling the wastegate in a turbocharged internal combustion engine including the steps of: determining, during a design phase, a control law which provides an objective opening of a controlling actuator of the wastegate according to the supercharging pressure; determining an objective supercharging pressure; measuring an actual supercharging pressure; determining a first open loop contribution of an objective position of a controlling actuator of the wastegate by means of the control law and according to the objective supercharging pressure; determining a second closed loop contribution of the objective position of the controlling actuator of the wastegate; and calculating the objective position of the controlling actuator of the wastegate by adding the two contributions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling the wastegatein a turbocharged internal combustion engine.

2. Description of the Related Art

Some internal combustion engines are provided with a turbochargersupercharging system, which can increase the power developed by theengine by exploiting the enthalpy of exhaust gases for compressing theair aspirated by the engine, and thus increasing volumetric intakeefficiency.

A turbocharger supercharging system typically includes a turbochargerprovided with a turbine, which is arranged along an exhaust pipe torotate at a high speed under the bias of the exhaust gases expelled bythe engine, and with a supercharger. The supercharger is rotated by theturbine and is arranged along the air feeding pipe to compress the airaspirated by the engine. In a turbocharger supercharging system, theoperating range of the turbocharger must be kept within a useful zonedepending on the crank position for both functional reasons (i.e. toavoid irregular or low efficiency operation) and for structural reasons(i.e. to avoid damaging the turbocharger). In order to be able to limitthe supercharging pressure (i.e. the pressure of the compressed airdownstream of the supercharger), a bypass pipe regulated by a wastegateis typically arranged in parallel to the turbine. When the wastegate isopened part of the exhaust gas flows along the bypass pipe, and thusbypasses the turbine, and this decreases the rotation speed of theimpeller, and thus decreases the supercharging.

A pneumatic actuator controlled by a regulating solenoid valve whichregulates the intervention of the wastegate is used to control thewastegate. The pneumatic actuator comprises a sealed shell, whichinternally supports a flexible membrane, which divides the sealed shellinto two reciprocally, fluid-tight chambers. The flexible membrane ismechanically connected to a rigid rod, which controls the wastegate forcontrolling the opening and closing of the wastegate itself. A firstchamber is connected to atmospheric pressure, while a second chamber isconnected to the supercharging pressure and is connectable toatmospheric pressure by means of a pipe regulated by the regulatingsolenoid valve of the proportional type, which is adapted to divide thepipe between a closed position, in which the pipe is completely closed,and a maximum opening position.

A contrast spring, which is compressed between a wall of the shell andthe flexible membrane, and which rests on the flexible membrane on theside opposite to the rod, is arranged in the first chamber. When thepressure difference between the two chambers is lower than anintervention threshold (determined by the preload of the contrastspring), the rod maintains the wastegate in a completely closedposition. When the pressure difference between the two chambers ishigher than the intervention threshold, the contrast spring starts tocompress under the bias of the flexible membrane, which is thusdeformed, determining a movement of the rod, which consequently movesthe wastegate towards the opening position. By controlling theregulating solenoid valve, the second chamber can be connected toatmospheric pressure with a variable introduction gap, and thus thepressure difference between the two chambers can be regulated, whichdifference, in turn, determines the opening or closing of the wastegate.It is worth noting that until the difference between the superchargingpressure and the atmospheric pressure exceeds the intervention threshold(equal to the preload generated by the contrast spring divided by theflexible membrane area), the wastegate cannot be opened by the actionexerted by the regulating solenoid valve (which can only reduce, and notincrease, the pressure difference between the supercharging pressure andatmospheric pressure).

In the internal combustion engines of the type generally known in therelated art, an objective supercharging pressure is generated, which isused to generate a control of the wastegate by adding an open loopcontribution and a closed loop contribution: the open loop contributionis generated using an experimentally obtained control map, while theclosed loop contribution is provided by a PID regulator. The PIDregulator attempts to cancel a pressure error, which is typicallyrepresented by the difference between the objective superchargingpressure and the actual supercharging pressure measured by a sensor.

However, the preload generated by the contrast spring of the pneumaticactuator has a high construction dispersion, a considerable thermaldrift and also a certain time drift. Furthermore, the pneumatic actuatorhas a considerable hysteresis. Thus, the behavior of the pneumaticactuator significantly varies between the opening movement and theopposite closing movement. Consequently, the map used for determiningthe closed loop contribution is strongly non-linear and the pursuing ofthe objective supercharging pressure is complicated. Thus, in internalcombustion engines of the type generally known in the related art, thepursuing of the objective supercharging pressure tends to have highovershoots or undershooting (i.e. the actual supercharging pressureeither exceeds or is even much lower than the objective superchargingpressure), and thus cause oscillations, particularly when thesupercharging pressure surrounds the intervention threshold under whichthe wastegate cannot be opened by the action exerted by the regulatingsolenoid valve.

Overshoots (i.e. peaks) of the supercharging pressure are particularlyannoying because they determine high strain (potentially dangerous intime) in the mechanical components of the internal combustion engine andbecause they may generate both noise perceivable by the vehicleoccupants and corresponding undesired oscillations of the torquegenerated by the internal combustion engine.

In order to reduce overshoots, it is possible to reduce the integrativecontribution of the PID regulator used to calculate the closed loopcontribution of the wastegate control. However, this solution makespursuing the objective pressure very slow (thus considerably increasesthe so-called turbo-lag) and often does not allow the system to reachthe objective supercharging pressure (i.e. the actual superchargingpressure tends to the objective supercharging pressure but never reachesit).

DE102004016011A1 describes a method for controlling a wastegate in aturbocharged internal combustion engine. This method contemplatesdetermining a first closed loop contribution HSR of an objectiveposition of a controlling actuator of the wastegate; determining asecond adaptive contribution OFHATLSTS of the objective position of thecontrolling actuator for the wastegate; calculating the objectiveposition HATLSTS of the controlling actuator of the wastegate by addingthe two contributions HSR and OFHATLSTS; and controlling the controllingactuator of the wastegate for pursuing the objective position HATLSTS ofthe controlling actuator of the wastegate.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a method forcontrolling a wastegate in a turbocharged internal combustion engine,where the control method is free from the above-described drawbacks, andspecifically, is easy and cost-effective to implement.

Thus, the present invention is directed toward a method for controllingthe wastegate in a turbocharged internal combustion engine including thesteps of: determining, during a design phase, a control law whichprovides an objective opening of a controlling actuator of the wastegateaccording to the supercharging pressure; determining an objectivesupercharging pressure; measuring an actual supercharging pressure;determining a first open loop contribution of an objective position of acontrolling actuator of the wastegate by means of the control law andaccording to the objective supercharging pressure; determining a secondclosed loop contribution of the objective position of the controllingactuator of the wastegate; and calculating the objective position of thecontrolling actuator of the wastegate by adding the two contributions.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will bereadily appreciated as the same becomes better understood after readingthe subsequent description taken in connection with the accompanyingdrawings wherein:

FIG. 1 is a diagrammatic view of an internal combustion engine includinga turbocharger and a control unit which implements the wastegate controlmethod of the present invention;

FIG. 2 is a diagrammatic view of a pneumatic actuator of the wastegate;

FIG. 3 is a chart illustrating different opening zones of the pneumaticactuator of the wastegate according to the supercharging pressure;

FIG. 4 is a chart which illustrates an experimental control map;

FIG. 5 is a block chart of a control logic of the wastegate;

FIG. 6 is a chart which illustrates the weight variation of an adaptivecontribution according to the position of the wastegate; and

FIG. 7 is a diagrammatic view of a variant of the pneumatic actuator ofthe wastegate in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

An internal combustion engine supercharged by means of a turbochargersupercharging system 2 is generally indicated at 1 in FIG. 1. In therepresentative embodiment illustrated here, the internal combustionengine 1 includes four cylinders 3, each of which is connected to anintake manifold 4 by means of at least one respective intake valve (notshown) and to an exhaust manifold 5 by means of at least one respectiveexhaust valve (not shown). The intake manifold 4 receives fresh air(i.e. air coming from the external environment) through an intake pipe6, which is provided with an air cleaner 7 and is regulated by abutterfly valve 8. An intercooler 9 for cooling the intake air may bearranged along the intake pipe 6. An exhaust pipe 10, which feeds theexhaust gases produced by the combustion to an exhaust system, isconnected to the exhaust manifold 5. The exhaust pipe 10 emits the gasesproduced by the combustion into the atmosphere and normally comprises atleast one catalyzer 11 and at least one muffler (not shown) arrangeddownstream of the catalyzer 11. Those having ordinary skill in the artwill appreciate from the description that follows that the internalcombustion engine 1 may include more than four cylinders 3 and thatthese cylinders may be arranged in-line, in a V-shape, or in any othersuitable configuration without departing from the scope of theinvention. In addition, the internal combustion engine 1 may includeother components as are commonly known in the related art.

The supercharging system 2 of the internal combustion engine 1 comprisesa turbocharger 12 provided with a turbine 13, which is arranged alongthe exhaust pipe 10 in order to rotate at high speed under the bias ofthe exhaust gases expelled from the cylinders 3, and a supercharger 14,which is arranged along the intake pipe 6 and is mechanically connectedto the turbine 13 in order to be rotatably fed by the turbine 13 itselfand thus increase the pressure of the air fed into the intake pipe 6.

A bypass pipe 15 is provided along the exhaust pipe 10. The bypass pipe15 is connected in parallel to the turbine 13 so that the ends thereofare connected upstream and downstream of the turbine 13 itself. Awastegate 16 is arranged along the bypass pipe 15 and is adapted toregulate the exhaust gas flow rate through the bypass pipe 15 and iscontrolled by a pneumatic actuator 17. A bypass pipe 18 is providedalong the exhaust pipe 10 and is connected in parallel to thesupercharger 14 so that the ends thereof are connected upstream anddownstream of the supercharger 14 itself. A Poff valve 19 is arrangedalong the bypass pipe 18 and is adapted to regulate the exhaust gaseswhich flow through the bypass pipe 18 and is controlled by an electricactuator 20.

The internal combustion engine 1 is controlled by an electronic controlunit 21, which governs the operation of all the components of theinternal combustion engine 1 including the supercharging system 2. Inparticular, the electronic control unit 21 controls the actuators 17 and20 of the wastegate 16 and of the Poff valve 19. The electronic controlunit 21 is connected to sensors 22, which measure the temperature andthe pressure along the intake pipe 6 upstream of the supercharger 14, tosensors 23, which measure the temperature and pressure along the intakepipe 6 upstream of the butterfly valve 8, and to sensors 24, whichmeasure the temperature and pressure inside the intake manifold 4.Furthermore, the electronic control unit 21 is connected to a sensor 25,which measures the angular position (and thus the rotation speed) of acrankshaft of the internal combustion engine 1, and to a sensor 26,which measures the timing of the intake and/or exhaust valves.

As shown in FIG. 2, the pneumatic actuator 17 of the wastegate 16includes a sealed shell 27, which externally supports a flexiblemembrane 28. The membrane 28 divides the sealed shell 27 into tworeciprocally isolated chambers 29 and 30. The flexible membrane 28 ismechanically connected to a rigid rod 31, which controls the wastegate16 for controlling the opening and closing of the wastegate 16 itself.Chamber 29 is connected by means of a pipe 32 to atmospheric pressure(taken upstream of the supercharger 14), while chamber 30 is connectedby means of a pipe 33 to supercharging pressure (taken downstream of thesupercharger 14) and is connected by means of a pipe 34 to atmosphericpressure (taken upstream of the supercharger 14). The pipe 34 is notfree, but it is instead regulated by a regulating solenoid valve 35,which is adapted to divide the pipe 34 between a closing position, inwhich the pipe 34 is completely closed, and a maximum opening position.

A contrast spring 36, which is compressed between a wall of the shell 27and the flexible membrane 28, and which rests on the flexible membrane28 on the side opposite to the rod 31, is arranged in the chamber 29.When the pressure difference between chamber 30 and chamber 29 is lowerthan an intervention threshold (determined by the preload of thecontrast spring 36), the rod 31 maintains the wastegate 16 in acompletely closed position, while when the pressure difference betweenchamber 30 and chamber 29 is higher than the intervention threshold, thecontrast spring 36 starts to compress under the bias of the flexiblemembrane 28, and is thus deformed, determining a movement of the rod 31,which consequently moves the wastegate 16 towards the opening position.By controlling the regulating solenoid valve 35, the second chamber 30can be connected to atmospheric pressure with a variable introductiongap, thus the pressure difference between the two chambers 29 and 30 canbe regulated. This pressure difference, in turn, determines the openingor closing of the wastegate 16.

It is worth noting that until the difference between the superchargingpressure P and the atmospheric pressure P_(atm) exceeds the interventionthreshold (which is equal to the preload generated by the contrastspring 36 divided by the area of the flexible membrane 28), thewastegate 16 cannot be opened by the action which is exerted by theregulating solenoid valve 35. The regulating solenoid valve 35 can onlyreduce and not increase the pressure difference between superchargingpressure P and atmospheric pressure P_(atm). Due to constructiondispersion, thermal drift and time drift, the preload generated by thecontrast spring 36 is known only with a rather high uncertainty (in theorder of ±20%). Consequently, three operating zones (shown in FIG. 3)are identified for the pneumatic actuator 17 of the wastegate 16according to the supercharging pressure P (or rather according to thedifference between supercharging pressure P and atmospheric pressureP_(atm)): a zone A operating at low supercharging pressure P (i.e. at alow supercharging ratio RP), in which the wastegate 16 remainssubstantially closed regardless of the action of the regulating solenoidvalve 35; a zone B operating at intermediate supercharging pressure P(i.e. at an intermediate supercharging ratio RP), in which there isuncertainty concerning the position of the wastegate 16 and thepossibility of controlling the position of the wastegate 16 by means ofthe regulating solenoid valve 35; and a zone C operating at highsupercharging pressure P (i.e. at a high supercharging ratio RP), inwhich the position of the wastegate 16 is controllable by the regulatingsolenoid valve 35.

Among other things, the electronic control unit 21 controls the positionof the wastegate 16 by controlling the regulating solenoid valve 35 ofthe pneumatic actuator 17. The control method used by the electroniccontrol unit 21 for controlling the position of the wastegate 16 bycontrolling the regulating solenoid valve 35 is described below.

During a design stage of the internal combustion engine 1, a control lawCL is determined experimentally and provides an objective opening WG ofthe regulating solenoid valve 35 of the wastegate 16 according to asupercharging pressure P (or rather according to a supercharging ratioRP which is equal to the supercharging pressure P and atmosphericpressure P_(atm) and is equivalent to the supercharging pressure P) andto a reduced mass flow rate M_(R) of the supercharger 14. In otherwords, the control law CL supplies the opening WG of the regulatingsolenoid valve 35 of the wastegate 16, which should allow a desiredsupercharging pressure P to be obtained (or rather a desiredsupercharging ratio RP) in presence of a given reduced mass flow rateM_(R). According to one embodiment shown by way of example in FIG. 4,the control law CL consists of an experimental map (i.e. a table orrather a matrix) which, as apparent in FIG. 4, is strongly linear.Alternatively, the control law CL may consist of an arithmeticalfunction. The control law CL is stored in a memory of the electroniccontrol unit 21 to be used as described below.

In use, during normal operation of the internal combustion engine 1, theelectronic control unit 21 measures the actual supercharging pressure P(i.e. the air pressure along the intake pipe 6 downstream of thesupercharger 14), measures or estimates (in known manner) atmosphericpressure P_(atm), and estimates (in known manner) the actual reducedmass air flow M_(R) of the supercharger 14. Furthermore, during normaloperation of the internal combustion engine 1, the electronic controlunit 21 determines in known manner an objective supercharging pressureP_(obj), which must be pursued by controlling, if needed, the regulatingsolenoid valve 35 of the wastegate 16. In order to control theregulating solenoid valve 35 of the wastegate 16, the electronic controlunit 21 determines an objective position WG_(obj) of the regulatingsolenoid valve 35 of the wastegate 16, which is generally actuated usingan open loop control.

As shown in FIG. 5, the objective position WG_(obj) of the regulatingsolenoid valve 35 of the wastegate 16 is calculated by algebraicallyadding four contributions while taking the sign into account: an openloop contribution WG_(OL), a closed loop contribution WG_(CL1), a closedloop contribution WG_(CL2), and an adaptive contribution WG_(A).

The open loop contribution WG_(OL) is determined using the control lawCL. An objective compression ratio RP_(obj) (equal to the ratio betweenobjective supercharging pressure P_(obj) and atmospheric pressureP_(atm) and equivalent to the objective supercharging pressure P_(obj))is determined according to the objective supercharging pressure P_(obj).Thus, the objective compression ratio RP_(obj) and the reduced mass flowrate M_(R) are supplied to a calculation block 37, which by using thecontrol law CL provides the open loop contribution WG_(OL).

Preferably, before being supplied to the calculating block 37, theobjective compression ratio RP_(obj) is filtered by means of afirst-order low-pass filter 38 to reduce the variation rapidity. Inother words, the objective compression ratio RP_(obj) is filtered bymeans of the low-pass filter 38 so as to slow down the evolution of theobjective compression ratio RP_(obj), thus “rounding off” possible stepvariations. The function of the low-pass filter 38 is to make theevolution of the objective compression ratio RP_(obj) more “real” (i.e.more adherent to what occurs in reality), because it is apparent thatstep (or in all case very fast) variations of the actual superchargingpressure P are not possible due to evident physical limits caused by theinvolved inertia. According to one embodiment, a cutoff frequency of thelow-pass filter 38 is determined according to the reduced mass flow rateM_(R) of the supercharger 14 and the actual supercharging ratio RPaccording to an experimentally determined law.

According to one embodiment, the open loop contribution WG_(OL) suppliedby the calculation block 37 is first compensated by means of threecompensation parameters K_(atm), K_(H2O) and K_(air), and then filteredby means of a first-order low-pass filter 39 to reduce the variationrapidity. The compensation parameter K_(air) is determined by acalculation block 40 according to the aspirated air temperature T_(air)and using a linear equation having experimentally determinedcoefficients. The compensation block K_(H2O) is determined by thecalculation block 41 according to the temperature T_(H2O) of a coolingliquid of the internal combustion engine 1 and using a linear equationhaving experimentally determined coefficients. The compensationparameter K_(atm) is determined by a calculation block 42 according tothe atmospheric pressure P_(atm) and using a linear equation havingexperimentally determined coefficients. The coefficients of the linearequation which provides the compensation parameter K_(atm) according tothe atmospheric pressure P_(atm) may not be constant but instead varyaccording to the reduced mass flow rate M_(R) of the supercharger 14 andthe actual supercharging ratio RP according to an experimentallydetermined law.

The open loop contribution WG_(OL) is filtered by means of the low-passfilter 39 so as to slow down the evolution of the open loop contributionWG_(OL), thus “rounding off” possible step variations. The function ofthe low-pass filter 39 is to make the evolution of the open loopcontribution WG_(OL) more “real” (i.e. more adherent to what occurs inreality), because it is apparent that step (or in all case very fast)variations of the position of the regulating of the solenoid valve 35are not possible due to evident physical limits caused by the involvedinertia. According to one embodiment, a cutoff frequency of the low-passfilter 39 is determined according to the actual supercharging ratio RPaccording to an experimentally determined law. According to oneembodiment, the open loop contribution WG_(OL) is asymmetricallyfiltered by means of the low-pass filter 39. The open loop contributionWG_(OL) is filtered by the low-pass filter 39 only when the open loopcontribution WG_(OL) varies to open the wastegate 16 and not when theopen loop contribution WG_(OL) varies to close the wastegate 16. In thismanner, the intervention of the supercharger 14 is faster (morereactive) favoring response promptness of the internal combustion engine1 (thus reducing turbo-lag), while the stopping of the supercharger 14is smoother. It is worth noting that when maximum performance is sought,an “abrupt” reaction of the internal combustion engine 1 is acceptable(and in some cases even desired), while in other cases a “smooth”behavior, i.e. without excessively rapid, forceful interventions, isdesired. It is worth noting that by virtue of the presence of thelow-pass filter 39 possible oscillating phenomena in the pneumaticactuator 17 of the wastegate 16 are either eliminated or greatlyattenuated. Such a result is obtained by virtue of the fact that theaction of the low-pass filter 39 avoids providing excessively rapidoscillations which could set off oscillatory phenomena to the flexiblemembrane 28 and to the contrast spring 36.

The closed loop contribution WG_(CL1) of the objective position WG_(obj)of the regulating solenoid valve 35 of the wastegate 16 is obtainedusing a virtual position WGF of the wastegate 16 (thus a controlmagnitude which has no precise correspondence with physical reality) asfeedback variable, which virtual position WGF is determined not by meansof a direct measurement by a real measuring sensor but by using thecontrol law CL as measuring sensor. In other words, a calculation block43 provides the virtual position WGF of the wastegate 16 by applying thecontrol law CL according to the actual supercharging pressure P (orrather the actual supercharging ratio RP) and the reduced mass flow rateM_(R) of the supercharger 14. Thus, the virtual position WGF of thewastegate 16 corresponds to the position that the wastegate should haveaccording to control law CL (and thus affected by all the errors ofcontrol law CL) in conjunction with the actual supercharging ratio RPand the actual reduced flow rate M_(R) of the compressor 14. The virtualposition WGF of the wastegate 16 is compared with the open loopcontribution WG_(OL) which corresponds to the position that thewastegate 16 should have according to the control law CL (and thusaffected by all the errors of the control law CL) in conjunction withthe actual compression ratio RP_(obj) and the actual reduced flow massM_(R) of the supercharger 14. In other words, the open loop contributionWG_(OL) is an objective of the virtual position WGF because it iscalculated using the objective compression ratio RP_(obj). Inparticular, a position error ε_(WG) is calculated by calculating thedifference between the open loop contribution WGOL of the objectiveposition WG_(obj) of the regulating solenoid valve 35 of the wastegate16 and the virtual position WGF of the wastegate 16 and such apositioning error ε_(WG) is supplied to a PID regulator 44 whichattempts to cancel the position error ε_(WG) itself.

The fact of comparing two values (the open loop contribution WG_(OL)which represents an objective of the virtual position WGF and thevirtual position WGF) obtained by the control law CL allows tocompensate the errors of the control law CL and to linearize thestrongly non-linear behaviour of the wastegate 16. In this manner, thePID regulator 44 may work more stably and the calibration of the controlparameters (i.e. of the proportional, integrative, derivativecoefficients and saturation thresholds) of the PID regulator 44 isrelatively simple. Furthermore, the control loop of the PID regulator 44is self-compensated according to the aspirated air temperature T_(air),to the temperature T_(H2O) of a cooling liquid of the internalcombustion engine 1, and to atmospheric pressure P_(atm).

The closed loop contribution WG_(CL2) of the objective position WG_(obj)of the regulating solenoid valve 35 of the wastegate 16 is determined byusing the supercharging pressure P as feedback variable. Thus, apressure error ε_(p) is calculated by determining the difference betweenthe objective supercharging pressure P_(obj) and the actualsupercharging pressure P and the pressure error ε_(WG) is supplied to aPID regulator 45 which attempts to cancel the pressure error ε_(WG)itself.

Preferably, before being compared with the actual supercharging pressureP, the objective supercharging pressure P_(obj) is filtered by means ofa first-order low-pass filter 46 to reduce variation rapidity. In otherwords, the objective supercharging pressure P_(obj) is filtered by meansof the low-pass filter 46 so as to slow down the evolution of theobjective supercharging pressure P_(obj) by “rounding off” possible stepvariations. The function of the low-pass filter 46 is to make theevolution of the objective supercharging pressure P_(obj) more “real”(i.e. more adherent to what occurs in reality), because it is apparentthat step (or in all case very fast) variations of the actualsupercharging pressure P are not possible due to evident physical limitscaused by the involved inertia. According to one embodiment, a cutofffrequency of the low-pass filter 46 is determined according to thereduced mass flow rate M_(R) of the supercharger 14 and of the actualsupercharging ratio RP according to an experimentally determined law.

In order to avoid negative interferences between the action of theregulator 44 and the action of the regulator 45, the dynamic of theregulator 44 is different from the dynamic of the regulator 45. Inparticular, the regulator 44 is essentially proportional and derivative(i.e. has high proportional and derivative coefficients and a lowintegral coefficient) in order to be ready (i.e. to work rapidly), whilethe regulator 45 is substantially integral (i.e. has low proportionaland derivative coefficients and a high integral coefficient) in order toguarantee the convergence between the objective supercharging pressureP_(obj) and the actual supercharging pressure P. Therefore, theregulator 44 is used to react rapidly and promptly to objectivesupercharging pressure variations P_(obj), while the regulator 45 isused to make the actual supercharging pressure P converge with theobjective supercharging pressure P_(obj) at the end of the transient.

The adaptive contribution WG_(A) of the objective position WG_(obj) ofthe regulating solenoid valve 35 of the wastegate 16 is substantially a“historical memory” of the previous actuations of the wastegate 16 andtakes the control interventions made in the past into account. Theadaptive contribution WG_(A) is stored in a memory 47 of the electroniccontrol unit 21 and is cyclically updated when the turbocharger 12 is atstable speed (e.g. when the reduced mass flow rate M_(R) of thesupercharger 14 and the supercharging ratio RP remain appropriatelyconstant for at least one interval of predetermined time) and using anintegral term of the PID regulator 45 and/or of the PID regulator 44.The adaptive contribution WG_(A) is substantially equal to an “average”of the past integral terms of the PID regulator 45 and/or of the PIDregulator 44 at stabilized running conditions of the turbocharger 12.The adaptive contribution WG_(A) stored in the memory 47 is updated whenthe turbocharger 12 is in stabilized running conditions, by using theintegral term of the PID regulator 45 and/or the PID regulator 44weighed by means of a weight W which substantially depends on an actualposition WG of the regulating solenoid valve 35 of the wastegate 16 sothat the weight W is minimum when the hysteresis of the wastegate 16 ismaximum (as shown in FIG. 6). In this manner, adaptivity is alwaysgradual (i.e. the last integral term of the PID regulator 45 and/or ofthe PID regulator 44 cannot upset the adaptive contribution WG_(A)stored in the memory 47) and loading values distorted by the hysteresisis avoided in the adaptive contribution WG_(A).

Generally, the adaptive contribution WG_(A) varies according to thereduced mass flow rate M_(R) of the supercharger 14 and of thesupercharging ratio RP. Furthermore, the adaptive contribution WG_(A) isfiltered by means of a first-order low-pass filter 48 to reducevariation rapidity. In other words, the adaptive contribution WG_(A) isnot supplied abruptly but is supplied gradually to avoid stepinterventions which never correspond to the physical reality and thus tofavor control convergence. According to one embodiment, the cutofffrequency of the low-pass filter 48 is constant. Alternatively, thecutoff frequency of the low-pass filter 48 could be varied according tothe reduced mass flow rate M_(R) of the supercharger 14 and of thesupercharging ratio RP.

With reference to FIG. 3, the electronic control unit 21 divides theoperation field of the wastegate 16 according to the actualsupercharging pressure P (or rather according to the difference betweensupercharging pressure P and atmospheric pressure P_(atm)) and in threedifferent operating zones: a zone A operating at low superchargingpressure P (named “NOT-ACTIVE”), in which the wastegate 16 remainssubstantially closed regardless of the action of the regulating solenoidvalve 35; a zone B operating at intermediate supercharging pressure P(named “PRE-ACTIVE”), in which there is uncertainty concerning theposition of the wastegate 16 and the possibility of controlling theposition of the wastegate 16 by means of the regulating solenoid valve35; and a zone C operating at high supercharging pressure P (named“ACTIVE”), in which the position of the wastegate 16 is controllable bythe regulating solenoid valve 35.

In use, the electronic control unit 21 avoids any type of control of theregulating solenoid valve 35 when the difference between the actualsupercharging pressure P and atmospheric pressure P_(atm) is in zone Aoperating at low supercharging pressure. Furthermore, in use, theelectronic control unit 21 differentiates the type of control accordingto whether the difference between the actual supercharging pressure Pand atmospheric pressure P_(atm) is in zone B operating at intermediatesupercharging pressure or in zone C operating at high superchargingpressure.

According to a first embodiment, operating parameters of the PIDregulators 44 and 45 are differentiated according to whether thedifference between the actual supercharging pressure P and atmosphericpressure P_(atm) is in zone B operating at intermediate superchargingpressure or in zone C operating at high supercharging pressure. Inparticular, in zone B operating at intermediate supercharging pressure aslower control is used with respect to the control used in zone Coperating at high supercharging pressure. Consequently, in zone Boperating at intermediate supercharging pressure smaller proportional,integrative and/or derivative coefficients of the PID regulators 44 and45 are used with respect to the similar coefficients used in zone Coperating at high supercharging pressure, and in zone B operating atintermediate supercharging pressure lower saturation thresholds are usedwith respect to the similar saturation thresholds used in zone Coperating at high supercharging pressure. A saturation thresholddetermines the freezing, i.e. the blocking, of the further increase of acorresponding proportional, integral or deviate terms when the termsitself exceeds the saturation threshold.

According to a different embodiment, only the open loop control is usedwhen the difference between the actual supercharging pressure P and theatmospheric pressure P_(atm) is in zone B operating at intermediatesupercharging pressure, and thus the closed loop contributions WG_(CL1)and WG_(CL2) are completely reset when the difference between the actualsupercharging pressure P and atmospheric pressure P_(atm) is in zone Boperating at intermediate supercharging pressure. According to a furtherembodiment, when the difference between the actual superchargingpressure P and the atmospheric pressure P_(atm) is in zone B operatingat intermediate supercharging pressure, a predetermined constant value,which is independent from the objective supercharging pressure P_(obj),is assigned to the objective position WG_(obj) of the regulatingsolenoid valve 35 of the wastegate 16. In other words, the fourcontributions WG_(OL), WG_(CL1), WG_(CL2) and WG_(A) are ignored and theobjective position WG_(obj) of the regulating solenoid valve 35 of thewastegate 16 is always constant independent from the objectivesupercharging pressure P_(obj).

The integral term of the PID regulators 44 and 45 contains in itself a“memory” of the errors which occurred in the immediate past. Thus, whenvariations to the surrounding conditions occur (e.g. passing from zone Coperating a high supercharging pressure to zone B operating atintermediate supercharging pressure, or in case of rapid variation, i.e.of strong transient, of the objective supercharging pressure P_(obj)),the “memory” of the errors which occurred in the immediate pastcontained in the integral term of the PID regulators 44 and 45 may havenegative effects because it represents a situation which is no longerpresent. In order to avoid the negative effects of the “memory” of theerrors which occurred in the immediate past contained in the integralterm of the PID regulators 44 and 45, the electronic control unit 21resets the integral term of the PID regulators 44 and 45 when the actualsupercharging pressure P decreases passing from zone C operating at highsupercharging pressure to zone B operating at intermediate superchargingpressure. Furthermore, the electronic control unit 21 resets (orpossibly “freezes”, i.e. prevents a further growth of) each integralterms of the PID regulators 44 and 45 in case of rapid variation, i.e.high transient, of the objective supercharging pressure P_(obj) if theintegral term itself is high, i.e. higher than the absolute value ofpredetermined threshold. In other words, when a rapid variation of theobjective supercharging pressure P_(obj) and an integral term of the PIDregulators 44 and 45 is higher in absolute value that a predeterminethreshold value, then the integral term itself is either reset or frozen(i.e. is not varied until the end of the high transient).

In order to establish when a high transient of the objectivesupercharging pressure P_(obj) is present (i.e. a rapid variation of theobjective supercharging pressure P_(obj)) the electronic control unit 21compares the objective supercharging pressure P_(obj) with the objectivesupercharging pressure P_(obj-F) filtered by a low-pass filter 49 todetermine a gradient ΔP_(obj) of an objective supercharging pressureP_(obj) which indicates the variation speed of the objectivesupercharging pressure P_(obj). In other words, the gradient ΔP_(obj) ofthe objective supercharging pressure P_(obj) is calculated bycalculating the difference between the objective supercharging pressureP_(obj) and the objective supercharging pressure P_(obj-F) filtered bythe low-pass filter 49. When the gradient ΔP_(obj) of the objectivesupercharging pressure P_(obj) is higher than a threshold value, thenthe electronic control unit 21 establishes the presence of a hightransient of the objective supercharging pressure P_(obj) (i.e. of arapid variation of the objective supercharging pressure P_(obj)) andthus resets (or possibly “freezes”) the integral terms of the PIDregulators 44 and 45. Such a threshold value may be according to thesupercharging ratio RP and the reduced mass flow rate M_(R) of thesupercharger 14. According to one embodiment, a cutoff frequency of thelow-pass filter 49 is determined according to the reduced mass flow rateM_(R) of the supercharger 14 and of the actual supercharging ratio RPaccording to an experimentally determined law.

According to a possible embodiment, when the actual superchargingpressure P passes from zone B operating at intermediate superchargingpressure to zone C operating at high supercharging pressure theelectronic control unit 21 intervenes on the low-pass filters 46 and 49using the actual supercharging pressure.

According to another possible embodiment, the electronic control unit 21learns a border supercharging pressure P_(BORDER) (shown in FIG. 3),under which the wastegate 16 remains substantially closed regardless ofthe control action of the regulating solenoid valve 35, and thusestablishes the borders of zone B operating at intermediatesupercharging pressure according to the difference between the bordersupercharging pressure P_(BORDER) and atmospheric pressure P_(atm)(typically zone B operating a intermediate supercharging pressure iscentered on the difference between the border supercharging pressureP_(BORDER) and atmospheric pressure P_(atm)). In other words, instead ofusing the design border supercharging pressure P_(BORDER) which has avery high uncertainty (indicatively ±20%), the electronic control unitlearns the real border supercharging pressure P_(BORDER) to attempt toreduce zone B operating at intermediate supercharging pressure to theminimum. It is worth noting that zone B operating an intermediatesupercharging pressure can never be eliminated (i.e. flow rate atpartially zero amplitude), because the learning of the real bordersupercharging pressure P_(BORDER) has in all cases a given error marginand in all cases the border supercharging pressure P_(BORDER) isaffected by thermal drift and time drift.

In order to learn the border supercharging pressure P_(BORDER) theelectronic control unit 21 completely closes the regulating solenoidvalve 35 of the wastegate 16 for a given interval of learning time inwhich the reduced mass flow rate M_(R) of the supercharger 14 exceeds apredetermined threshold value. The border supercharging pressureP_(BORDER) is substantially assumed as equal to the actual maximumsupercharging pressure P during the interval of learning time.

According to one embodiment, the electronic control unit 21 varies theintegral coefficients of the PID regulators 44 and 45 according to thepressure error ε_(P), so as to vary the control features according tovariations of the pressure error ε_(P). In particular, the electroniccontrol unit 21 varies the integral coefficients of the PID regulators44 and 45 in manner inversely proportional to the pressure error ε_(P)so that the higher the integral coefficients of the PID regulators 44and 45, the smaller the pressure error ε_(P), and varies theproportional coefficients of the PID regulators 44 and 45 in mannerdirectly proportional to the pressure error ε_(P) so that the higher theproportional coefficients of the PID regulators 44 and 45, the higherthe pressure error ε_(P). In other words, the integral term of the PIDregulators 44 and 45 (directly proportional to the integral coefficientsof the PID regulators 44 and 45) is used to guarantee the convergencebetween the actual supercharging pressure P and the objectivesupercharging pressure P_(obj), but such a convergence is reached interms of a transient when the pressure error ε_(P) is relatively small.At the beginning of the transient when the pressure error ε_(P) ishigher, the integral terms of the PID regulators 44 and 45 may generateoscillations and thus in order to avoid such a risk the integralcoefficients of the PID regulators 44 and 45 are reduced at thebeginning of the transient when the pressure error ε_(P) is high. Theopposite applies to the proportional terms of the PID regulators 44 and45 (directly proportional to the proportional and derivativecoefficients of the PID regulators 44 and 45), which must be higher whenthe pressure error ε_(p) is high to ensure response speed and must belower when the pressure error ε_(P) is low to ensure convergence.

In the above described low-pass filters 38, 46 and 49, the cutofffrequency is determined according to the reduced mass flow rate M_(R) ofthe supercharger 14 and of the actual supercharging pressure RP.According to an equivalent embodiment, the cutoff frequency isdetermined according to the rotation speed of the internal combustionengine 1 and according to a gear engaged in a transmission whichreceives motion from the internal combustion engine 1. In this regard,it is worth noting that the dynamic of the supercharger 12 clearlyvaries according to the engaged gear, because the increase of revolutionspeed of the internal combustion engine 1 is rapid in lower gears, thusthe increase of speed of revolution of the supercharger 12 is equallyrapid. Instead, in high gears, the increase of revolution speed of theinternal combustion engine 1 is slow, thus the increase of speed ofrevolution of the supercharger 12 is equally slow.

Similarly, the threshold value with which the gradient ΔP_(obj) of theobjective supercharging pressure P_(obj) is compared to establish if ahigh transient of the objective supercharging pressure P_(obj) ispresent may depend on the reduced mass flow rate M_(R) of thesupercharger 14 and the actual supercharging ratio RP or may depend onthe rotation speed of the internal combustion engine 1 of a gear engagedin a transmission which receives motion from the internal combustionengine 1.

It should be further noted that the supercharging pressure P and thesupercharging ratio RP are perfectly equivalent to one another, becausethe atmospheric pressure P_(atm) is approximately constant and has avalue approximating a unitary value. Thus using the supercharging ratioRP is equivalent to using the supercharging pressure P and vice versa.In the control chart shown in FIG. 5 and described above, thesupercharging ratio RP is used, but according to an equivalentembodiment the supercharging pressure P may be used instead of thesupercharging ratio RP.

In the embodiment described above, the control law CL provides anobjective opening WG of the regulating solenoid valve 35 of thewastegate 16 according to a supercharging pressure P (or rather asupercharging ratio RP, which is equal to the supercharging pressure Pand atmospheric pressure P_(atm) and is equivalent to the superchargingpressure P) and of a reduced mass flow rate M_(R) of the supercharger14. According to an equivalent embodiment, the control law CL providesan objective opening WG of the regulating solenoid valve 35 of thewastegate 16 either according to a power delivered by the internalcombustion engine 1 and a volumetric efficiency of the internalcombustion engine 1, or according to a rotation speed of the internalcombustion engine 1 and a volumetric efficiency. Obviously, differentcombinations of the parameters of the internal combustion engine 1 arepossible.

According to a different embodiment shown in FIG. 7, the pneumaticactuator 17 no longer contemplates the pipe 33 which connects thechamber 30 to the supercharging pressure (taken upstream of thesupercharger 14). Furthermore, the pneumatic actuator 17 comprises avacuum source 50 (i.e. a vacuum pump) which is connected to theregulating solenoid valve 35 by means of a pipe 51. In this manner, thechamber 30 of the shell 27 is connectable by means of the regulatingsolenoid valve 35 to atmospheric pressure by means of the pipe 34 or tothe source 50 by means of the pipe 51. In this manner, by controllingthe regulating solenoid valve 35 a pressure even lower than atmosphericpressure can be imposed in the chamber 30. Then, the control of theposition of the wastegate 16 is always active, i.e. with reference toFIG. 3, zone A in which the wastegate 16 is insensitive to the action ofthe regulating solenoid valve 35 no longer exists. In this embodiment,the control is always active because the wastegate 16 is alwayssensitive to the action of the regulating solenoid valve 35. Inparticular, in zone B the control is always closed loop and may havemore reactive values to reduce the reply delay of the supercharger 12.

Preferably, in this embodiment, the wastegate 16 is normally openinstead of being normally closed as in the embodiment shown in FIG. 2.

The control method of the wastegate 16 above described has manyadvantages. The control method of the wastegate 16 described above issimple and cost-effective to implement in a control unit of an internalcombustion engine because it only uses measurements supplied by sensorswhich are always present in modern internal combustion engines and doesnot require either high calculation capacity or high memory capacity.Furthermore, the control method of the wastegate 16 described aboveallows to obtain a particularly robust control of the wastegate 16,ready and free from oscillations in all operating conditions.

The invention has been described in an illustrative manner. It is to beunderstood that the terminology which has been used is intended to be inthe nature of words of description rather than of limitation. Manymodifications and variations of the invention are possible in light ofthe above teachings. Therefore, the invention may be practiced otherthan as specifically described.

What is claimed is:
 1. A method for controlling the wastegate (16) in ainternal combustion engine (1) turbocharged by means of a turbocharger(12); the control method comprises the steps of: determining anobjective supercharging pressure (P_(obj)); measuring an actualsupercharging pressure (P); determining a second closed loopcontribution (WG_(CL1)) of an objective position (WG_(obj)) of acontrolling actuator (35) of the wastegate (16); determining a thirdadaptive contribution (WG_(A)) of the objective position (WG_(obj)) ofthe controlling actuator (35) of the wastegate (16); calculating theobjective position (WG_(obj)) of the controlling actuator (35) of thewastegate (16) by adding the two contributions (WG_(OL), WG_(CL1));controlling the controlling actuator (35) of the wastegate (16), so asto pursue the objective position (WG_(obj)) of the controlling actuator(35) of the wastegate (16); determining, during a design phase, acontrol law (CL) which provides an objective opening of a controllingactuator (35) of the wastegate (16) according to the superchargingpressure (P); determining a first open loop contribution (WG_(OL)) of anobjective position (WG_(obj)) of the controlling actuator (35) of thewastegate (16) through the control law (CL) and according to theobjective supercharging pressure (P_(obj)); and calculating theobjective position (WG_(obj)) of the controlling actuator (35) of thewastegate (16) by adding the three contributions (WG_(OL), WG_(CL1),WG_(A)).
 2. The control method as set forth in claim 1 further includingthe steps of: storing the third adaptive contribution (WG_(A)) in amemory (47); and updating the third adaptive contribution (WG_(A))stored in the memory (47) when the turbocharger (12) is in a stabilizedrunning condition and using an integral term of the second regulator(45) and/or of the first regulator (44).
 3. The control method as setforth in claim 2 further including the steps of: determining a weight(W); and updating the third adaptive contribution (WG_(A)), when theturbocharger (12) is in a stabilized running condition, using theintegral term of the second regulator (45) and/or of the first regulator(44) weighed by means of the weight (W).
 4. The control method as setforth in claim 3 further including the step of determining the weight(W) according to an actual position of the controlling actuator (35) ofthe wastegate (16), so that the weight (W) is minimum when thehysteresis in the control of wastegate (16) is maximum.
 5. The controlmethod as set forth in claim 1, wherein the third adaptive contribution(WG_(A)) is variable according to a reduced mass flow rate (M_(R)) ofthe supercharger (14) and to a supercharging ratio (RP) which is equalto the ratio between the supercharging pressure (P) and the atmosphericpressure (P_(atm)).
 6. The control method as set forth in claim 1further including the step of filtering the third adaptive contribution(WG_(A)) by means of a second first-order low-pass filter (48) in orderto reduce the variation rapidity.
 7. The control method as set forth inclaim 1 further including the step of filtering the objectivesupercharging pressure (P_(obj)) by means of a first first-orderlow-pass filter (38, 46) in order to reduce the variation rapidity. 8.The control method as set forth in claim 7 further including the step ofdetermining a cutoff frequency of the first low-pass filter (38, 46)according to a reduced mass flow rate (M_(R)) of the supercharger (14)and to a supercharging ratio (RP) which is equal to the ratio betweenthe supercharging pressure (P) and the atmospheric pressure (P_(atm)) oraccording to a rotation speed of the internal combustion engine (1) andaccording to a gear engaged in a transmission which receives motion fromthe internal combustion engine (1).